Snakes have blood flowing over their eyes. Technically, you do, too. But in your case, that blood is contained within the tiny blood vessels that send oxygen and nutrients to your eyelids. Eyelids that blink keep us from being blinded by the blood vessels and tissues making up our eyelids, while still allowing the eyelid to do its job. When you blink, your eyelids help keep dust and debris out of your eyes while keeping the surface moist.